It is known to employ encapsulated fragrance compositions in consumer products, including household care, personal care, and fabric care products. Perfume compositions are encapsulated for a variety of reasons. Encapsulation isolates and protects perfume ingredients from external suspending media, such as consumer product bases, in which they may be incompatible or unstable. Microcapsules can also be used to increase the efficiency with which perfume ingredients are deposited onto substrates, such as skin, hair, fabrics or hard household surfaces, as well as acting as a means of controlling the spatio-temporal release of perfume.
Aminoplast microcapsules are among the most commonly used encapsulating media for perfume compositions. There are established processes of forming aminoplast microcapsules that are well documented in the prior art. Typically, in a first step an oil-in-water emulsion is formed, consisting of fragrance-containing oil droplets dispersed in an aqueous continuous phase. Thereafter, shell-forming amino-aldehyde pre-condensates contained in the emulsion are caused to form encapsulating polymeric shells around the perfume-containing droplets to form core-shell microcapsules.
Reagents and reaction conditions are selected to ensure the amino-aldehyde pre-condensates undergo poly-condensation and crosslinking to form polymeric shells rapidly around the oil droplets, thereby retaining all, or substantially all, of the perfume ingredients within the droplets and preventing subsequent leakage of encapsulated perfume ingredients from the microcapsules. If the shells are unable to form quickly then it may be impossible to form microcapsules, or if microcapsules can be formed they may be characterized by poor fragrance retention and may be prone to agglomeration.
It is conventional to employ polymers as colloidal stabilizers during microcapsule formation. The polymers function in several ways: They ensure that stable oil-in-water emulsions are formed; they ensure that pre-condensates and cross-linking agents are present at the oil-water interface in high concentration; and they provide a template around which the pre-condensates and cross-linking agents can react to form the encapsulating polymeric shells.
Colloidal stabilizers employed in the preparation of aminoplast microcapsules are anionic or non-ionic polymers, see for example U.S. Pat. No. 8,119,587. Particularly effective colloidal stabilizers are acrylic acid-based copolymers bearing sulphonate groups. Examples of these copolymers are available commercially under the brand LUPASOL (ex BASF), such as LUPASOL PA 140, or LUPASOL VFR. These commercial polymers are exemplary colloidal stabilizers, which are widely employed in the preparation of commercial aminoplast microcapsule compositions. Encapsulated perfume compositions formed using these polymeric stabilizers exhibit a good balance between perfume retention during storage, and perfume performance when deposited on a substrate.
Aminoplast microcapsules prepared by the process described above are typically collected in the form of a slurry comprising a plurality of microcapsules suspended in a suitable suspending medium. The microcapsule slurry may then be used directly in applications, or further processed in a manner known per se. For example, it is conventional to post-coat aminoplast microcapsules with a cationic water-soluble polymer in order to provide them with a net positive charge, the purpose of which coating is to act as a deposition aid and increase the affinity of the microcapsules to substrates of interest, whether that is fabric, or keratinous substrates such as hair or skin, and thereby increase the substantivity of encapsulated perfume ingredients on those surfaces.
Aminoplast microcapsules represent a very popular means of encapsulating perfume compositions because they are highly stable, that is, they are able to efficiently retain fragrance within their cores, both during microcapsule formation and subsequently during storage. Furthermore, they can also bring perfumery benefits to consumer products that would be unattainable by applying neat fragrance directly to a consumer product base.
However, whilst it is expected that an encapsulated perfume composition should deliver leakage stability and perfume benefits in consumer products, in order for customers to perceive these compositions favourably, they must also be easy to use, that is, they should be easy for a customer to handle, store, transport, and the like. More particularly, they should be compatible with, as well as easily and inexpensively incorporated into, consumer product bases. If a customer cannot perform these tasks easily and cost-effectively, the encapsulated perfume composition will not be favourably received.
During the development of an encapsulated perfume composition in the form of a slurry of aminoplast microcapsules, the applicant encountered a problem when attempting to incorporate the slurry into consumer product bases, and more particularly consumer product bases containing cationic surfactants, most notably fabric softener or fabric conditioner bases and hair conditioner bases. More particularly, when attempting to incorporate the slurries into cationic bases, the microcapsules were observed to agglomerate, forming unsightly and disturbing aggregates that could not be dispersed with dilution and/or vigorous stirring.
The applicant set out to address this incorporation problem, and surprisingly found that replacing a conventional anionic sulphonate-containing polymeric stabilizer, with an alternative polymer bearing polyatomic cations, as a colloidal stabilizer, it was not only possible to form a stable microcapsule slurry that provide excellent perfume benefits when deposited on substrates, but it was also possible to incorporate the slurry into a consumer product base, and particularly cationic bases used in fabric conditioners and hair conditioners without any signs of the agglomeration problem.
The applicant was also surprised to find that whereas one might expect a colloidal stabilizer to be substantially washed into the continuous phase during microcapsule formation, sufficient amounts of it were retained and embedded in the microcapsule shells such that the microcapsules were found to bear a positive charge sufficient to ensure that the microcapsules exhibited a high affinity to substrates without it being necessary to carry out conventional post-coating of the microcapsules with cationic deposition aids.